We are studying small intestinal transport and its regulation. Stimuli that enhance and suppress total intestinal absorption and specific absorption per unit of mucosa are being examined. Stimuli include diabetes, intestinal resection, alterations in composition of diet, and dietary restriction. Substrates under investigation include hexoses, amino acids, sodium, calcium and magnesium. Absorption is measured in vivo by luminal perfusion of the entire small intestine for determining total intestinal absorption. Individual intestinal sites are perfused to determine the intestinal locus of maximal enhancement and suppression of absorption. Absorption kinetics are measured at the site of maximal adaptation. Intestinal function and its response to stimuli is correlated with crypt cell proliferation rate, mucosal cell transit time from crypt cell to villus tip, and synthesis and degradation of protein by mucosal absorptive cells. Protein synthesis by mucosal cells is utilized to identify transport proteins. BIBLIOGRAPHIC REFERENCES: Miller, D. L., and Schedl, H. P.: Effects of Experimental Diabetes on Intestinal Strontium Absorption in the Rat. Proc. Soc. Exp. Biol. Med., 152:589-592, 1976. Petith, M. M., and Schedl, H. P.: Intestinal Adaptation to Dietary Calcium Restriction: In vivo Cecal and Colonic Calcium Transport in the Rat. Gastroenterology, 71:1039-1042, 1976.